1. Field of Invention
This invention relates to the control of vending machines, and particularly to the control of vending machines having a large number of actuators for vending a large quantity or a wide variety of products. The invention also relates to the diagnosis of operating defects in the vending machine, particularly defects in the actuators.
2. Description of the Prior Art
Most vending machines today employ brute force type selection circuits and blocker circuits to prevent more than one actuator from being actuated at a time. A typical blocker circuit comprises a group of single pole, double throw blocker switches each associated with one of the actuators and actuated by a cam which is rotated during that actuator's cycle. When all of the actuators are at their "home" or normal start-stop position, the switches are connected in series and supply a signal which enables a second set of switches, the selection switches. Typically, each selection switch is a single pole double throw switch associated with a single actuator. All of the selection switches are connected in series until one selection switch is actuated, causing it to interrupt the series connection of selection switches and apply current to the associated actuator. Once a selection is made and the selected actuator begins to move, its cam causes the associated blocker switch to move to its other position closing its hold contacts so that it supplies current to the selected actuator for the remainder of an actuator cycle. The interruption of the series connection of blocker switches through the blocker contacts disables the selection circuit so that no other actuators can be started until the originally selected actuator has completed its cycle.
It has been recognized for some time that the type of blocker circuit described above has a major disadvantage: when an actuator is disabled in mid-cycle, the entire vending machine is disabled. An actuator can be disabled as a result of an actuator defect, or as a result of a jam in the vending apparatus itself or of the product it is intended to vend. Although attempts have been made to circumvent this problem (see, for example, U.S. Pat. No. 4,220,235), they have employed relatively expensive components associated with each actuator and, therefore, have not been very practical, especially in machines having a large number of actuators.